[单调栈 扫描线] BZOJ 4826 [Hnoi2017]影魔

先用单调栈找出比i大的第一个数li 和 ri
然后[i,i+1]有p1的贡献 [li,ri]有p1的贡献
[li,x] x∈[i+1,ri−1] 有p2的贡献
[x,ri] x∈[li+1,i−1] 有p2的贡献
放在平面上就是点和线段 矩形求和 扫描线

#include<cstdio>#include<cstdlib>#include<algorithm>using namespace std;typedef long long ll;inline char nc(){  static char buf[100000],*p1=buf,*p2=buf;  return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;}inline void read(int &x){  char c=nc(),b=1;  for (;!(c>='0' && c<='9');c=nc()) if (c=='-') b=-1;  for (x=0;c>='0' && c<='9';x=x*10+c-'0',c=nc()); x*=b;}const int N=200005;int n,a[N];namespace BIT{  int maxn; ll c1[N],c2[N];  inline void init(int n){    maxn=n; for (int i=1;i<=n;i++) c1[i]=c2[i]=0;  }  inline void add(int x,int r){    for (int i=x;i<=maxn;i+=i&-i)      c1[i]+=r,c2[i]+=(ll)x*r;  }  inline void add(int l,int r,int t){    add(l,t); add(r+1,-t);  }  inline ll sum(int x){    ll ret1=0,ret2=0;    for (int i=x;i;i-=i&-i)      ret1+=c1[i],ret2+=c2[i];    return ret1*(x+1)-ret2;  }  inline ll sum(int l,int r){    return sum(r)-sum(l-1);  }}struct event{  int f,x,y1,y2,z;  event(int f=0,int x=0,int y1=0,int y2=0,int z=0):f(f),x(x),y1(y1),y2(y2),z(z) { }  bool operator < (const event &B) const{    return x==B.x?f<B.f:x<B.x;  }}ev[N<<3];int tot;int p1,p2;int sta[N],pnt;int l[N],r[N];int Q,_l[N],_r[N];ll ans[N];int main(){  freopen("t.in","r",stdin);  freopen("t.out","w",stdout);  read(n); read(Q); read(p1); read(p2);  for (int i=1;i<=n;i++) read(a[i]);  for (int i=1;i<=Q;i++) read(_l[i]),read(_r[i]);  pnt=0;  for (int i=1;i<=n;i++){    while (pnt && a[sta[pnt]]<a[i]) pnt--;    l[i]=sta[pnt]; sta[++pnt]=i;  }  pnt=0;  for (int i=n;i;i--){    while (pnt && a[sta[pnt]]<a[i]) pnt--;    r[i]=sta[pnt]; sta[++pnt]=i;  }  for (int i=1;i<=n;i++) if (!r[i]) r[i]=n+1;  tot=0;  for (int i=1;i<n;i++)    ev[++tot]=event(1,i,i+1,i+1,p1);  for (int i=1;i<=n;i++){    if (l[i]!=0 && r[i]!=n+1)      ev[++tot]=event(1,l[i],r[i],r[i],p1);    if (l[i]!=0)      if (i+1<=r[i]-1)    ev[++tot]=event(1,l[i],i+1,r[i]-1,p2);  }  for (int i=1;i<=Q;i++)    ev[++tot]=event(2,_l[i]-1,_l[i],_r[i],i),ev[++tot]=event(3,_r[i],_l[i],_r[i],i);  BIT::init(n);  sort(ev+1,ev+tot+1);  for (int i=1;i<=tot;i++)    if (ev[i].f==1)      BIT::add(ev[i].y1,ev[i].y2,ev[i].z);    else if (ev[i].f==2)      ans[ev[i].z]-=BIT::sum(ev[i].y1,ev[i].y2);    else      ans[ev[i].z]+=BIT::sum(ev[i].y1,ev[i].y2);  tot=0;  for (int i=1;i<=n;i++)    if (r[i]!=n+1)      if (l[i]+1<=i-1)    ev[++tot]=event(1,r[i],l[i]+1,i-1,p2);  for (int i=1;i<=Q;i++)    ev[++tot]=event(2,_l[i]-1,_l[i],_r[i],i),ev[++tot]=event(3,_r[i],_l[i],_r[i],i);  BIT::init(n);  sort(ev+1,ev+tot+1);  for (int i=1;i<=tot;i++)    if (ev[i].f==1)      BIT::add(ev[i].y1,ev[i].y2,ev[i].z);    else if (ev[i].f==2)      ans[ev[i].z]-=BIT::sum(ev[i].y1,ev[i].y2);    else      ans[ev[i].z]+=BIT::sum(ev[i].y1,ev[i].y2);  for (int i=1;i<=Q;i++)    printf("%lld\n",ans[i]);  return 0;}